<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        // Number 转换成数字
        var str = 2021 +Number("2023")
        console.log(str)
        // parseInt 取整 js里面字符串拼接 直接用+号
        var a = parseInt("4.513") + 2000
        alert(a)
        var b = 2023
        document.write(b.toString())
        // document中换行<br/>
        document.write("你好 <br/> 明天")
        alert("蓝桥 \n yunke")
    </script>
</body>
</html>